Improve the image size in the documentation (#1045)

- Images included using the figure directive: default to 100%
- Single images included by calling Figure.show(): max-width is 80%.
- Gallery thumbnails: max-width is 100%. 

I also add a thin box for each gallery thumbnail and center the thumbnail titles.

Author: seisman

doc/_static/style.css

@@ -38,10 +38,6 @@ p {
     margin-bottom: 50px;
 }
 
-.rst-content img {
-    max-width: 80%;
-}
-
 .sidebar-title {
     margin-top: 10px;
     margin-bottom: 0px;
@@ -167,3 +163,13 @@ a.copybtn {
     font-weight: bold;
     font-style: italic;
 }
+
+/* Style for images and thumbnails of sphinx-gallery */
+.sphx-glr-thumbcontainer {
+    border: solid #d6d6d6 1px!important;
+    text-align: center!important;
+}
+
+.sphx-glr-single-img {
+    max-width: 80%!important;
+}

doc/overview.rst

@@ -43,6 +43,7 @@ These are conference presentations about the development of PyGMT (previously
 
 .. figure:: https://img.youtube.com/vi/SSIGJEe0BIk/maxresdefault.jpg
     :target: https://www.youtube.com/watch?v=SSIGJEe0BIk
+    :width: 80%
     :align: center
     :alt: ROSES 2020 youtube video
 
@@ -54,6 +55,7 @@ These are conference presentations about the development of PyGMT (previously
 
 .. figure:: _static/agu2019-poster.jpg
    :target: https://doi.org/10.6084/m9.figshare.11320280
+   :width: 80%
    :align: center
    :alt: AGU 2019 poster on figshare
 
@@ -65,6 +67,7 @@ These are conference presentations about the development of PyGMT (previously
 
 .. figure:: _static/scipy2018-youtube-thumbnail.png
    :target: https://www.youtube.com/watch?v=6wMtfZXfTRM
+   :width: 80%
    :align: center
    :alt: SciPy youtube video
 
@@ -76,6 +79,7 @@ These are conference presentations about the development of PyGMT (previously
 
 .. figure:: _static/aogs2018-poster.jpg
    :target: https://doi.org/10.6084/m9.figshare.6399944
+   :width: 80%
    :align: center
    :alt: AOGS poster on figshare
 
@@ -87,6 +91,7 @@ These are conference presentations about the development of PyGMT (previously
 
 .. figure:: _static/scipy2017-youtube-thumbnail.png
    :target: https://www.youtube.com/watch?v=93M4How7R24
+   :width: 80%
    :align: center
    :alt: SciPy youtube video
 
@@ -98,5 +103,6 @@ These are conference presentations about the development of PyGMT (previously
 
 .. figure:: _static/agu2017-poster.jpg
    :target: https://doi.org/10.6084/m9.figshare.5662411
+   :width: 80%
    :align: center
    :alt: AGU 2017 poster on figshare