Tone down theme to neutral system-style buttons and subtle accents

Buttons use light grey background with borders instead of bright blue.
Tab selection uses dark text instead of blue highlight. Focus borders
toned down to grey. Bump version to 1.4.0.

Author: achrafsoltani

src/utils/constants.py

@@ -1,7 +1,7 @@
 # Application constants
 
 APP_NAME = "Merisio"
-APP_VERSION = "1.3.1"
+APP_VERSION = "1.4.0"
 FILE_EXTENSION = ".merisio"
 FILE_FILTER = "Merisio Projects (*.merisio);;All Files (*)"
 MSD_FILE_EXTENSION = ".msd"

src/utils/theme.py

@@ -132,8 +132,8 @@ def get_stylesheet() -> str:
 
     QTabBar::tab:selected {{
         background-color: {COLORS['bg_main']};
-        color: {COLORS['primary']};
-        border-bottom: 2px solid {COLORS['primary']};
+        color: {COLORS['text_primary']};
+        border-bottom: 2px solid {COLORS['text_secondary']};
         margin-bottom: -1px;
     }}
 
@@ -163,24 +163,26 @@ def get_stylesheet() -> str:
 
     /* Push Buttons */
     QPushButton {{
-        background-color: {COLORS['primary']};
-        color: white;
-        border: none;
-        padding: 8px 16px;
-        border-radius: 6px;
+        background-color: {COLORS['bg_sidebar']};
+        color: {COLORS['text_primary']};
+        border: 1px solid {COLORS['border']};
+        padding: 6px 14px;
+        border-radius: 4px;
     }}
 
     QPushButton:hover {{
-        background-color: {COLORS['primary_hover']};
+        background-color: {COLORS['bg_hover']};
+        border-color: #BBBFC4;
     }}
 
     QPushButton:pressed {{
-        background-color: {COLORS['primary']};
+        background-color: #D0D0D0;
     }}
 
     QPushButton:disabled {{
-        background-color: {COLORS['border']};
+        background-color: {COLORS['bg_main']};
         color: {COLORS['text_muted']};
+        border-color: {COLORS['border_light']};
     }}
 
     /* Line Edit */
@@ -194,7 +196,7 @@ def get_stylesheet() -> str:
     }}
 
     QLineEdit:focus {{
-        border-color: {COLORS['primary']};
+        border-color: {COLORS['text_secondary']};
     }}
 
     /* Text Edit */
@@ -207,7 +209,7 @@ def get_stylesheet() -> str:
     }}
 
     QTextEdit:focus {{
-        border-color: {COLORS['primary']};
+        border-color: {COLORS['text_secondary']};
     }}
 
     /* Combo Box */