# Different Plot Legend Style in the Plot with same code and How to make it good-looking inside the figure

I use Plot to draw two figures and combine them in one figure with the following code.

C1 = Plot[{((3 t + 1/2)^2 (1 - 2 t 1/4))/(18 t) + 2 t^3 (1)^2 (1/4)^3}, {t, 1/6 (3 - Sqrt), 2},
PlotTheme -> "Scientific", PlotRange -> Automatic, FrameLabel -> {{HoldForm[SubsuperscriptBox["\[Pi]", "i", "*"] // DisplayForm], None}, {HoldForm[t], None}},
LabelStyle -> {GrayLevel}, PlotStyle -> {Red},
PlotLegends -> {"\!$$\*SubsuperscriptBox[\(\[Pi]$$, $$A$$, $$*$$]\) \under \!$$\*SubscriptBox[\(\[Alpha]$$, $$A$$]\)=1"}]

D1 = Plot[{((3 t - 1/2)^2 (1 - 2 t (1/4)))/(18 t) + 2 t^3 (1)^2 (1/4)^3}, {t, (1/6) (3 - \[Sqrt]3), 2},
PlotTheme -> "Scientific", PlotRange -> Automatic, FrameLabel -> {{HoldForm[SubsuperscriptBox["\[Pi]", "i", "*"] // DisplayForm], None}, {HoldForm[t], None}}, PlotStyle -> {Dashed, Red},
PlotLegends -> {"\!$$\*SubsuperscriptBox[\(\[Pi]$$, $$B$$, $$*$$]\) \under \!$$\*SubscriptBox[\(\[Alpha]$$, $$B$$]\)=1"}]

Show[C1, D1, PlotRange -> All]


However, the font styles of the plot legend are different as shown in the picture even if I used the same PlotLegends in the code and I have tried LegendMaker and autoLegendto make the legend look nice but failed. How can I adjust or rewrite the code to make the plot legends look the same or achieve the effect of autoplot putting the legends on the right-bottom side of the figure? Thanks in advance.

In addition, how can I put the plot legend in the rounded rectangle with a grey background-color as shown in the example picture below? An alternative that allows to put the legend in the lower right corner (or everywhere for that matter):

Plot[{((3 t + 1/2)^2 (1 - 2 t 1/4))/(18 t) +
2 t^3 (1)^2 (1/4)^3, ((3 t - 1/2)^2 (1 - 2 t (1/4)))/(18 t) +
2 t^3 (1)^2 (1/4)^3}, {t, 1/6 (3 - Sqrt), 2},
PlotTheme -> "Scientific", PlotRange -> All,
FrameLabel -> {HoldForm[t],
HoldForm[SubsuperscriptBox["\[Pi]", "i", "*"] // DisplayForm]},
PlotStyle -> {Red, {Dashed, Red}},
PlotLegends ->
Placed[LineLegend[{"\!$$\*SubsuperscriptBox[\(\[Pi]$$, $$A$$, \
$$*$$]\) under \!$$\*SubscriptBox[\(\[Alpha]$$, $$A$$]\)=1",
"\!$$\*SubsuperscriptBox[\(\[Pi]$$, $$B$$, $$*$$]\) under \
\!$$\*SubscriptBox[\(\[Alpha]$$, $$B$$]\)=1"},
LegendLayout ->
Function[{x}, Grid[x, Spacings -> {0.6, 0}, Alignment -> Left]],
LegendMarkerSize -> {22, 12}], {0.8, 0.2}]] The last parenthesis in the Placed command controls where you want the legend to appear.

To add a box around the legend, as requested in the comments, use:

Plot[{((3 t + 1/2)^2 (1 - 2 t 1/4))/(18 t) +
2 t^3 (1)^2 (1/4)^3, ((3 t - 1/2)^2 (1 - 2 t (1/4)))/(18 t) +
2 t^3 (1)^2 (1/4)^3}, {t, 1/6 (3 - Sqrt), 2},
PlotTheme -> "Scientific", PlotRange -> All,
FrameLabel -> {HoldForm[t],
HoldForm[SubsuperscriptBox["\[Pi]", "i", "*"] // DisplayForm]},
PlotStyle -> {Red, {Dashed, Red}},
PlotLegends ->
Placed[LineLegend[{"\!$$\*SubsuperscriptBox[\(\[Pi]$$, $$A$$, \
$$*$$]\) under \!$$\*SubscriptBox[\(\[Alpha]$$, $$A$$]\)=1",
"\!$$\*SubsuperscriptBox[\(\[Pi]$$, $$B$$, $$*$$]\) under \
\!$$\*SubscriptBox[\(\[Alpha]$$, $$B$$]\)=1"},
LegendLayout ->
Function[{x}, Grid[x, Spacings -> {0.6, 0}, Alignment -> Left]],
LegendMarkerSize -> {22, 12},
LegendFunction -> (Framed[#,
FrameStyle -> Directive[Thickness[.05]], RoundingRadius -> 4,
Background -> RGBColor[.95, .95, .95, 1]] &)], {0.75, 0.2}]] • LegendLayout Function is useful to adjust the plot legend, but I still want to put the legends into a rounded rectangle with a grey background color as shown in the picture added later. Do you have a good idea to realize this? Thx Dec 15, 2020 at 7:12

Use a single Plot

Clear["Global*"]

Plot[{
((3 t + 1/2)^2 (1 - 2 t 1/4))/(18 t) + 2 t^3 (1)^2 (1/4)^3,
((3 t - 1/2)^2 (1 - 2 t (1/4)))/(18 t) + 2 t^3 (1)^2 (1/4)^3}, {t,
1/6 (3 - Sqrt), 2},
PlotTheme -> "Scientific",
PlotRange -> All,
FrameLabel -> {HoldForm[t],
HoldForm[SubsuperscriptBox["π", "i", "*"] // DisplayForm]},
PlotStyle -> {Red, {Dashed, Red}},
PlotLegends -> {
"\!$$\*SubsuperscriptBox[\(π$$, $$A$$, $$*$$]\) under \
\!$$\*SubscriptBox[\(α$$, $$A$$]\)=1",
"\!$$\*SubsuperscriptBox[\(π$$, $$B$$, $$*$$]\) under \
\!$$\*SubscriptBox[\(α$$, $$B$$]\)=1"}]
` 